Ecological Interaction Strengths Vary Through Time: How Temperature and Species Composition Affects the Diet of Three Groundfish Predators in the Gulf of Alaska

Multispecies models that incorporate predation often include some important assumptions regarding predator-prey dynamics. Generally, predation is assumed to be a function of prey availability and prey size alone. However, environmental factors, such as temperature, can affect interspecies dynamics by altering behavior and activity of both predators and prey. Furthermore a predator can influence another predatory species, either decreasing consumption rates (competition) or increasing foraging success (facilitation). Using a time series of trawl and stomach data I tested if predator length, prey availability, temperature and other predators’ densities affect the diets of Pacific cod (Gadus macrocephalus), Pacific halibut (Hippoglossus stenolepis), and sablefish (Anoplopoma fimbria) in the Gulf of Alaska (GOA). I investigated diet composition with multivariate approaches as well as focusing on one prey of ecological and commercial interest, walleye pollock (Theragra chalcogramma), with univariate statistics. In both diet composition and consumption of walleye pollock, we found evidence that ecological interaction strengths among these predators vary through time.  Temperature affected diet in some predators, but other predator densities were found to influence diets more consistently, indicating that inter- and intra-predator effects may be an important factor in structuring prey consumption. Furthermore, prey availability was generally not found to predict consumption of prey, particularly with walleye pollock. Incorporation of more complex species interactions that we observed in the diet data into models may yield additional insights into the system as species compositions and environmental factors change through time.